Page:Popular Science Monthly Volume 68.djvu/300

296 hyphæ stowed away in her buccal pocket, spits it out soon after completing her chamber, manures with her excreta the rapidly growing hyphæ and carefully weeds them till her firstling brood of workers hatches. These then bring into the nest the pieces of leaves and the vegetable detritus essential to the maintenance and growth of the garden. The extraordinary habits of one of these fungus-raising ants, Atta sexdens, have been recently studied in great detail by Jakob Huber, from whose valuable paper I borrow a number of the accompanying illustrations (Figs. 2 to 7).

Very different is the condition of certain queen ants poorly endowed with food-tissue—especially of some whose bodies are actually smaller than the largest workers of their species. Such queens are quite unable to bring up colonies unaided. They are therefore compelled, after fertilization, to associate themselves with adult workers either of their own or of a closely allied species. In the former case the queens may either remain in the parental nest and omit the nuptial flight, or return to the parental or to some other colony of the same species. In either case they add to the reproductive energy of an already established colony and thus prolong its life. If one of these poorly endowed queens, however, happens to alight from her nuptial journey far from any colony of her own species, she is obliged to associate with alien workers. And in this case, according to the species to which she belongs, one of three courses is open to her.

First, she may secure adoption in a small queenless colony of an allied species. Here she is fed, lays her eggs and the resulting larvae are reared by the strange workers. Eventually the alien workers die off and leave the queen and her own workers as an independent and sufficiently established colony, capable of rapid and often enormous multiplication. This is temporary social parasitism, first observed by myself in some of our American ants, but since found in some of the European species where I predicted its occurrence.

Second, the poorly endowed queen may establish herself in a colony of another species, but be unable, even after her workers have matured, to survive the death of the host colony, except, perhaps, by migrating to another nest of the same species. This is permanent social parasitism.

Third, the queen may enter a small colony of alien workers, and, when attacked, massacre them, appropriate their larvae and pupa?, carefully secrete and nurse them till they hatch and thus surround herself with a colony of young and loyal workers that can bring up her brood for her without any drain on her food-tissues. This is the method of colony formation adopted by queens of the slave-making ants, as I have found by a number of experiments during the past summer. These queens thus manifest an instinct, hitherto supposed to be exclusively peculiar to the workers, namely the instinct to rob the larvæ and pupæ of another species and bring them up as auxiliaries, or slaves.